Apparatus and method for conversion of animal litter biomass into useful energy

ABSTRACT

A method of converting animal litter biomass into useful energy includes the steps of both combusting and pyrolising the biomass, of mixing the resultant combustible gas from the pyrolysis step with the gases from the combustion step, of igniting the mixture of gases ad and feeding the hot mixture of gases to a thermal recuperator; and apparatus therefor.

CROSS REFERENCE TO RELATED APPLICATION

Benefit of U.S. Provisional Application for Patent Ser. No. 60/795,572,filed on Apr. 28, 2006, is hereby claimed.

FIELD OF THE INVENTION

The present invention relates to the conversion of animal litter biomassinto useful energy.

More specifically, the invention has particular, but not exclusive,reference to such conversion of poultry litter that essentially consistsof a mixture of wood shavings, straw and fecal matter. The expression‘poultry’ as used herein means domestic foul of various kinds, interalia chickens, turkeys, ducks and geese. The invention mayadvantageously be used for the conversion of biomass derived from thekeeping of other farm animals, such as pigs and bovines.

BACKGROUND OF THE INVENTION

Great emphasis is now placed by both government and the general publicupon the need to reduce the disposal of waste that might otherwiseprovide useful feedstock for varied processes in industry and generally.Recycling of metals, plastics and paper is now mandatory in manycountries to ensure that the optimum utilization of waste materials maybe achieved by reuse in appropriate processes. Equally, attention hasbeen focused upon so called renewable energy resources to provide ‘greenpower’ and among such resources biomass constitutes a major elementsince agricultural waste is a continuous and renewable source of fuel inthe right process. Many and varied techniques have been proposed andindeed adopted on a commercial basis for the destruction of poultrylitter biomass to produce energy by heat generation and/or gasificationfor use on site or for distribution to appropriate facilities for use.

Generally, techniques of this kind involve relatively complex plant, forexample fluidized bed combustors using bubbling bed technology, orgasifiers, and necessarily incur high capital and running costs.

Accordingly, there is a need for a simpler and therefore cheaperapproach to the conversion of animal litter biomass into useful energy.

SUMMARY OF THE INVENTION

It is therefore a general object of the present invention to provide amethod of and apparatus for the conversion of animal litter biomass intouseful energy.

A further object of the present invention is to provide such a methodand apparatus that employ relatively simple process steps and equipmentof comparatively simple construction with concomitant cost benefits.

According to a first aspect of the present invention there is provided amethod of converting animal litter biomass into useful energy comprisingthe steps of feeding said biomass in comminuted form into a primarycombustion zone comprising an upper region and a lower region, partiallycombusting the biomass at the lower region thereof at an elevatedtemperature in the presence of a combustion-sustaining medium thereby toprovide heat into the upper region thereof for pyrolysis to generatecombustible gases, of subjecting the lower partially combustedincandescent biomass to air flow to generate combustion gases, of mixingthe combustion gases and the combustible gases, of igniting theresultant mixture of gases thereof to produce a hot gaseous product, andof passing the hot gaseous product to a thermal recuperator forexpending and exploiting the heat energy thus produced.

The solid residue arising from combustion and pyrolisation is dischargedand may be employed further, for example for collection for use inhorticultural or agricultural applications.

The mixing of the gaseous products before their egress from the processseeks to secure the suppression of pollutants by heat destruction andenhanced rate of combustion.

According to a second aspect of the present invention there is providedan apparatus for the conversion of animal litter biomass into usefulenergy, the apparatus comprising a primary combustion zone incorporatinga chamber of frusto-conical form, a feed entry to the primary combustionzone, a feed conduit contiguous with said zone and connected to the feedentry at a relatively upper part of the zone, a combustible gas outletfor the primary pyrolysis combustion zone, a rotatable grate situated atthe base of the primary combustion zone, a means for rotating the grate,a combustion-sustaining fluid distributor located at said base, asecondary normal combustion zone on the grate circumscribing the base ofthe primary pyrolysis combustion zone, a combustion exhaust gas outletfrom the secondary combustion zone, a gas mixing zone downstream of thecombustible gas outlet and the combustion exhaust gas outlet wherein inuse the respective combustion gases and the combustible gas mix, anignition station for the resultant mixture of gases, the gas mixing zonecomprising at least a partial tube bank for reheating and suppression ofpollutant emissions, and a final gas discharge flue for the resultantgases.

Conveniently, the gas mixing zone includes a heat exchange zone forexpending and exploiting the heat energy of the hot mixture thusproduced.

The apparatus may be of generally cylindrical form.

Conveniently, there is also provided a means of comminuting thefeedstock which may include a hopper with a rotating armature providedwith blades suitable for effecting the break up of the animal litterbiomass introduced thereto. A rotatable disc may be disposed beneath thehopper outlet for feeding the comminuted feedstock into the feedconduit.

The combustion-sustaining medium distributor may be of foraminousconical form enclosing a plenum chamber therebeneath to which a suitableconduit for the medium, e.g. air, is connected.

The gas mixing zone may be provided with a full tube bank of coiledtubes or may in the alternative have a demi-bank of coiled tubesextending substantially half way around the zone.

Other objects and advantages of the present invention will becomeapparent from a careful reading of the detailed description providedherein, with appropriate reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects and advantages of the present invention will becomebetter understood with reference to the description in association withthe following Figures, in which similar references used in differentFigures denote similar components, wherein:

FIG. 1 is a diagrammatic vertical cross section of an apparatus for theconversion of animal litter biomass in accordance with the presentinvention;

FIG. 2 is a horizontal section taken through one embodiment of theapparatus shown in FIG. 1;

FIG. 3 is a horizontal section taken through an alternative embodimentof the apparatus shown in FIG. 1; and

FIG. 4 is a fragmented view on the line 4-4 in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the annexed drawings the preferred embodiment of thepresent invention will be herein described for indicative purpose and byno means as of limitation.

Referring first to FIG. 1 there is shown diagrammatically an apparatus 1for the conversion of animal litter biomass into useful energy, theapparatus including a generally hollow cylindrical body 2 enclosing aprimary combustion zone 4 of frusto-conical form vertically orientedcentrally within the body 2, the zone 4 having an upper region 5 a and alower region 5 b. The zone 4 has connected at its top part a feed tube 6which registers with an opening 7 in the top 8 of the body 2.

A feed hopper 10 is disposed vertically above the opening 7 and has arotatable drive spindle 9 carrying a plurality of comminuting paddles11; the hopper 10 has an outlet 13 feeding onto a rotating feed table 14provided with a discharge station 15 selectively aligned with theopening 7 and the outlet 13. In use feedstock, namely the biomass, isfed into the hopper 10 wherein it is comminuted prior to delivery to thecombustion zone 4.

Alternatively, as it would be obvious to one skilled in the art, thefeedstock, typically fed from a conveyor (not shown), can be directedinto the hopper 10 free of any spindle 9 and paddles 11, or evendirectly fed into the feed tube 6 through opening 7, without deviatingfrom the scope of the present invention.

At the base of the combustion zone 4 there is provided a circularrotatable grate 20 the diameter of which is greater than the basedimension of the zone 4 which is spaced therefrom to provide a path inuse for the centrifugal conveyance of incandescent biomass. The biomasslocated in the upper region of the combustion zone 4 is heated and driedby the heat generated by the incandescent biomass to form a pyrolysiszone. At the center of the grate 20 is a foraminous conical plenumchamber 22 for the introduction of air into the combustion zone 4, anair inlet pipe 24 being connected thereto and extending therefrom theexterior of the body 2. A drive shaft 26 for the grate 20 extendsthrough the pipe 24 for rotating the grate. A solid waste collectionarea 30 is defined beneath the rotatable grate 20 and a discharge outlet32 is provided for that area and leads to a removal station 34.

A secondary, normal combustion zone 40 is defined externally of theprimary zone 4 and is provided with perforated air distributor tubes orsparge pipes 42 to provide air for the combustion.

Both the zones 4 and 40 are contained within a central cylindrical core50, which is provided with suitable outlets 52 and 54 respectively forsaid zones, a gas discharge conduit 53 connecting the zone 4 to theoutlet 52.

A gas mixing chamber 60 is defined between the core 50 and the wall ofthe body 2 at the exit from the zones 4 and 40 and in this chamber thegases arising from pyrolysis and the combustion zones are mixed. Thencethe mixture of gases flows through into a heat exchange zone 59including a tube bank 61 formed in the annular space between the core 50and the wall of the body 2. In FIG. 2 the post-combustion zone tube bank61 extends substantially throughout the whole of the annular space, thetubes 61′ being held in tube plates 63 and being disposed in spacedrelation one to the other with baffles 62′ accommodated within theinterstices between the tubes. The successive baffles 62′ arealternately raised and lowered along the tubes 61′ to force the hotgaseous product to vertically flow through the tubes 61′, as illustratedby the alternating orientations of arrows around the baffles 62′ in FIG.2. In FIG. 3 the annular space is only partially, e.g. half, filled witha demi-tube bank 61 with tubes 61″, the remainder of the space beingprovided with offset baffles 62″. Baffles 62′ and 62″, essentiallyvertically oriented, are provided as shown to enhance in practice theturbulence of gases and to lengthen residence to time thereby tooptimize the various steps of mixing and suppression of noxiousemissions and heat transfer efficiency.

In use comminuted poultry litter biomass is fed from the hopper 10 intothe feed tube 6 of the combustion zone 4 and descends onto the grate 20and forms a bed of biomass typically extending up into the tube as shownin order to prevent heat losses there through. The temperature of thezone 4 is initially raised to a level appropriate for the ignition ofthe biomass and air is provided through the plenum 22. The biomass isburned only at the bottom (lower region 5 b) of the zone (smotheredcombustion) and that combustion energy allows the pyrolysis phenomenonin the biomass column thereabove (upper region 5 a), and the hot gasesof pyrolysis exit therefrom through the conduit 53 and the outlet 52into the mixing chamber 60.

An incandescent layer or cake of biomass gradually radiates on therotating grate 20 to pass from the pyrolysis zone 4 into the normalcombustion zone 40 supplied with air through sparge pipes 42, the gasbeing generated passing through the outlet 54 into the mixing chamber 60after providing more energy to the biomass in zone 4 for pyrolysis.

In the embodiment of FIG. 2 the gas from zone 4 and the combustion gasesemanating from zone 40 are mixed in the chamber 60 and pass through thetubes 61′ of the substantially full tube bank 61. The gases after theirpassage through the tubes 61′ enter into a further, ignition chamber 68,separated from the mixing chamber 60 by separation wall 67, providedwith a pilot flame igniter 69 and any remaining unburnt gas is combustedand all the gases from the chamber 68 pass over the tubes 61′, therebyeffectively reheating the mixture of gases from pyrolysis zone 4 andthose from combustion zone 40 passing through the tubes, thus improvingefficiency and contributing to the destruction of any harmful elementsthat might give rise to atmospheric pollution. All gaseous products ofcombustion exhaust through a common outlet 70 of the body 2 whence theypass to a thermal recuperator (not shown) for appropriate usage.

In the embodiment of FIG. 3 the tube bank 61 is not so long but thegases from zones 4 and 40 are again mixed in chamber 60 and pass throughthe tubes 61″. The mixture of gases then flow through a zone in whichturbulence is promoted by the baffles 62″ and eventually enter anignition chamber 68 wherein any remaining unburnt gas is ignited by theigniter 69. The resulting gas exhausts from the chamber 68 into a space71 (FIG. 4) defined over the offset baffles 62″ before flowing aroundthe tubes 61″ of the tube bank 61 to provide reheat for the gasespassing therethrough for the same purpose as described above in relationto FIG. 2, the final mixture of gases then exhausting through outlet 70for passage to a thermal recuperator.

The baffles are provided to improve turbulence and simultaneouslyincrease residence time of the gases to enhance heat transfer and theconsumption of potentially noxious elements in the gases.

The present invention thus provides a relatively simple and yeteffective means of disposing of a waste biomass product in a useful‘green’ energy way, thus reducing the time and cost of conventionaldisposal.

Although the present invention has been described with a certain degreeof particularity, it is to be understood that the disclosure has beenmade by way of example only and that the present invention is notlimited to the features of the embodiments described and illustratedherein, but includes all variations and modifications within the scopeand spirit of the invention as hereinafter claimed.

We claim:
 1. A method of converting animal litter biomass into usefulenergy, said method comprising the steps of: feeding said biomass incomminuted form into a primary combustion zone comprising an upperregion and a lower region; partially combusting the biomass at the lowerregion of the primary combustion zone at an elevated temperature in thepresence of a combustion-sustaining medium thereby to provide heat intothe upper region thereof for pyrolysis to generate combustible gases;subjecting partially combusted incandescent biomass in the lower regionto air flow to generate combustion gases; mixing the combustion gasesand the combustible gases in a mixing chamber; igniting the resultantmixture of gases thereof to produce a hot gaseous product; and passingthe hot gaseous product to a thermal recuperator for expending andexploiting the heat energy thus produced.
 2. The method of claim 1,wherein the incandescent biomass is combusted in a further combustionzone surrounding the zone and the combustion gases therefrom are mixedwith the combustible gases from the pyrolysis of the biomass.
 3. Themethod of claim 1, wherein the hot gaseous product passes to a heatexchange zone wherein it is caused to undergo heat exchange with themixture of gases from the mixing chamber.
 4. The method of claim 3,wherein turbulence is imparted to the flow of gases within the heatexchange zone by the provision of baffles thereby to lengthen theresidence time of gases within the zone and to enhance both thesuppression of noxious elements within the gases and the heat transferefficiency.
 5. An apparatus for the conversion of animal litter biomassinto useful energy, the apparatus comprising: a primary combustion zoneincorporating a chamber of frusto-conical form; a feed entry to theprimary combustion zone; a feed conduit contiguous with said primarycombustion zone and connected to the feed entry at a relatively upperregion of the primary combustion zone; a combustible gas outlet for theprimary pyrolysis combustion zone formed in the upper region; arotatable grate situated at the lower region of the primary combustionzone; a means for rotating the grate; a combustion-sustaining fluiddistributor located at the lower region; a secondary normal combustionzone on the grate circumscribing the lower region of the primarypyrolysis combustion zone; a combustion exhaust gas outlet from thesecondary combustion zone; a gas mixing zone downstream of thecombustible gas outlet and the combustion exhaust gas outlet wherein inuse the respective combustion gases and the combustible gas mix; anignition station for the resultant mixture of gases, the gas mixing zonecomprising at least a partial tube bank for reheating and suppression ofpollutant emissions; and a final gas discharge flue for the resultantgases.
 6. The apparatus of claim 5, wherein gas mixing zone includes aheat exchange zone for expending and exploiting the heat energy of thehot mixture thus produced.
 7. The apparatus of claim 5, wherein theapparatus is of generally cylindrical form.
 8. The apparatus of claim 5,wherein comminuting means is provided for comminuting the biomassfeedstock.
 9. The apparatus of claim 8, wherein the comminuting meanscomprises a hopper with a rotatable armature provided with blades. 10.The apparatus of claim 9, wherein a rotatable disc is disposed beneathoutlet of the hopper for feeding the comminuted feedstock into the feedconduit.
 11. The apparatus of claim 5, wherein the combustion-sustainingfluid medium distributor is of foraminous conical form incorporating aplenum chamber with a medium feed conduit connected thereto.
 12. Theapparatus of claim 6, wherein the gas mixing zone comprises a full tubebank of coiled tubes.
 13. The apparatus of claim 6, wherein the gasmixing zone comprises a demi-tube bank of coiled tubes.
 14. Theapparatus of claim 6, wherein baffles are provided in the heat exchangezone.
 15. The apparatus of claim 5, wherein a solid waste collectionarea is defined beneath the rotatable grate, and a discharge outlet isprovided therefor and leads to a removal station.
 16. The apparatus ofclaim 5, wherein the secondary normal combustion zone is definedexternally of the primary combustion zone, the secondary zone beingprovided with air distributor tubes.